Recent hadron therapy techniques for treating cancers make it possible to deliver a dose precisely on a target volume, for example a tumor, while preserving the surrounding tissue. A hadron therapy installation generally comprises a particle accelerator producing a beam of charged particles, a rotary gantry comprising transport means for the beam, and an irradiation unit. The irradiation unit delivers a dose distribution on the target volume and generally comprises means for monitoring the delivered dose, for example such as an ionization chamber, as well as means for monitoring the direction or shape of the beam.
The rotary gantry is capable of rotating about a horizontal axis of rotation, such that the irradiation unit can deliver a treatment beam at several irradiation angles. The rotary gantries of the traditional hadron therapy installations are generally designed to rotate 360° about a horizontal axis of rotation.
The rotary irradiation unit protrudes in a treatment chamber through a passage at least partially closed by a moving floor. This moving floor facilitates therapist access to the patient completely safely, while allowing the irradiation unit to rotate. Different models of moving floors have been developed.
Document U.S. Pat. No. 7,997,553 describes a hadron therapy installation comprising a rotary gantry that supports a beam transport line ending with an irradiation unit. A treatment chamber comprises a passage for the irradiation unit, which is covered at the floor of the treatment chamber by a moving floor. This floor comprises a plurality of moving panels positioned next to each other. During rotation of the gantry, each of these moving panels is actuated individually between a first position freeing the passage for an irradiation unit and a second position covering the passage around the irradiation unit. Such a floor requires means for monitoring the movement of a plurality of panels synchronously with the rotation of the gantry. These panels must be able to retract and extend in a short enough amount of time to avoid a collision between the irradiation unit and one of the panels on the one hand, and to avoid a risk of accident due to opening of the passage around the irradiation unit during an excessively long period of time on the other hand. Based on the angular position of the irradiation unit, an empty space may still exist between the irradiation unit and one of the panels of the four.
Document WO2010/076270 also describes a hadron therapy installation comprising a gantry that can rotate about a horizontal axis and supporting a beam transport line ending with an irradiation unit. A treatment chamber comprises a horizontal floor overhung by a cylindrical roof. The irradiation unit penetrates that treatment chamber through a transverse passage, which allows a 360° rotation of the irradiation unit about said horizontal axis. A moving floor closes said passage while forming a planar access surface at the floor of the treatment chamber, and a cylindrical separating wall at the roof. The proposed moving floor is made up of a main floor and two secondary floors each comprising a plurality of rigid transverse plates flexibly linked to each other. The main floor is driven by the gantry and the secondary floors are driven by the irradiation unit. The configuration of said moving floor completely closes the passage over 360° in any position of the irradiation unit. Other moving floor configurations are discussed in this same document, which is incorporated by reference into this application.
Document WO2010/076270 also describes a mechanism for connecting the secondary floors to the irradiation unit. This mechanism comprises two pairs of traction rails arranged on either side of the irradiation unit. Each of the two secondary floors comprises at least one pivot joint slidably guided in one of said pairs of traction rails. The pair of traction rails guides said pivot joint along a rectilinear path transverse to the direction of movement of the moving floor, and thus allows the moving floor to turn between the circular part and the straight part of the guide structure. Each of the traction rails is also part of a buffer mechanism that makes it possible to absorb a residual movement of the irradiation unit, when one of the secondary floors is accidentally immobilized. In a first embodiment, this buffer mechanism assumes the form of a deformable parallelogram comprising, for each rail, a member fastened to the irradiation unit, a member parallel to the rail, and a member parallel to the member fastened to the irradiation unit. The piston is connected between the traction rail and the member parallel to the traction rail. As long as the compression force transmitted by the piston remains below a threshold value, the piston forms a rigid transmission element. If the compression force transmitted by the piston exceeds the threshold value, the piston contracts and the deformable parallelogram is flattened, thus absorbing a residual movement of the irradiation unit when the floor connected to the deformable parallelogram is immobilized. In a second embodiment of this buffer mechanism, each end of a traction rail is connected to the irradiation unit by means of a piston. The buffer mechanism then comprises at least 4 pistons, preferably 8 pistons. The pistons comprise a load cell and are capable of contracting in case of immobilization of the moving floor to absorb a residual rotational movement of approximately 3° to 5° of the rotary gantry after an emergency stop command of the gantry transmitted by the load cell to the monitoring system of the hadron therapy installation. The present invention also aims to improve the connection of moving floor segments to the irradiation unit, in particular by reducing the number of mechanical parts around the irradiation unit, by freeing space around the irradiation unit to allow the placement of new accessories on the irradiation unit, and still further reducing the risk of immobilization of the moving floor in its guide structure.
The traditional hadron therapy installations require considerable space, and their on-site assembly is generally fairly labor-intensive. In order to reduce the costs related in particular to space constraints, new, more compact installations have been presented. The document “Gantries” by E. Pedroni Center for Proton Radiation Therapy—Paul Scherrer Institute—WE Chiba Jan. 5, 2010, describes most of the hadron therapy installations comprised in the state of the art, as well as a more compact installation developed by PSI and called “PSI Gantry 2”. This installation comprises a rotary gantry whereof the rotation about the horizontal axis of rotation is limited between two extreme angular positions of −30° and +180°. These angles are measured relative to a vertical plane comprising the axis of rotation, where an angle of 0° corresponds to the angular position in which the delivery line of the beam is at its highest position. (This convention for measuring angular positions of the rotary gantry and/or the irradiation unit supported by said rotary gantry will be maintained hereafter.)
Document EP 2308561 A1 describes another compact hadron therapy installation comprising a rotary gantry capable of rotating about a horizontal axis of rotation between two extreme angular positions of −35° and +190°.
These compact hadron therapy installations with an amplitude of rotation much lower than 360° must also be equipped with a floor, both for safety reasons and for accessibility reasons with respect to the patient. The known moving floors of the traditional hadron therapy installations (with an amplitude of rotation of 360°) could also be implemented on a compact hadron therapy installation. It is, however, more advantageous to use a floor system offering easier access around the patient, for example allowing the introduction of imaging means or means for monitoring the position of the patient.
Document U.S. Pat. No. 7,348,579 describes a hadron therapy installation whereof the gantry is capable of rotating about a horizontal axis of rotation between two angular positions comprised between 0° and 180°. The installation comprises a treatment chamber with a passage for the irradiation unit and a device capable of covering the passage irrespective of the position of the irradiation unit.
The filer of this application recently announced the launch of a smaller proton therapy system allowing lateral access to the treatment chamber. This installation comprises a rotary gantry capable of rotating about a horizontal axis of rotation between two angular positions comprised between −30° and 190°. For this very compact installation, a treatment floor is developed in the form of a deformable band guided in a guide structure that requires a reduced installation volume. However, for such a compact moving floor solution, the risk of immobilization of the moving floor is particularly high.
Consequently, the first problem at the base of the present invention is to propose a hadron therapy installation comprising: an irradiation unit with a horizontal axis of rotation capable of rotating around a treatment area between a first angular position (α), situated above the treatment area, and a second angular position (β), situated below said treatment area; and moving floor in the form of a deformable band guided in a guide structure, which requires a reduced installation volume, provides excellent access to the patient, and has a relatively low risk of immobilization.